An ancient mechanism called a "Chinese windlass" is an example of a device that achieves a mechanical advantage using spools of different diameters. This device can be used to a lift bucket of water from a well. It consists of a rope that is wound around two spools of slightly different diameters that share a common shaft. A pulley that is attached to a water bucket is located in the loop of rope between the two spools. The spools are wound in opposite directions so that rotating the shaft causes the rope to unwind from one spool as the other takes it up. If the spools were exactly the same diameter, turning the shaft would result in no change in the vertical position of the pulley since the rope unwound from one spool would exactly match that taken up by the other. However, because the spools have different diameters, the pulley will in fact move in response to the shaft rotation. The typical arrangement gives a large mechanical advantage, which means that a relatively small torque acting over a large number rotations can lift a large weight of water. The large mechanical advantage also means that friction of the bearings is sufficient to prevent backward rotation of the shaft from the weight of the bucket. A similar arrangement is used today in differential hoists such as those found in automotive repair shops.
The new mechanism turns the function of a Chinese windlass upside-down, in that it is designed to give a large rolling motion from a small linear motion. The new mechanism is ideal for use in a roller damper for controlling air flow. There are several different designs of dampers in the prior art. Problems with the existing designs include:
1) large force requirements PA0 2) high cost PA0 3) relatively small flow areas PA0 4) high leakage rates PA0 5) relatively long actuator movement required
A more complete description of prior art appears in the current ASHRAE handbook.
Another excellent use of the mechanism is as a sun shade. Sun shades are normally manually operated. Various systems for automatically operating a sunshade are available, but they are clumsy and expensive.
The device can also be of great value in physical training. Existing training systems usually require massive and cumbersome weights to provide the proper force. Spring devices can be used, but they may not give the proper force characteristics. The new mechanism can give great flexibility in forces using relatively small weights or springs.
An additional use of the mechanism is as an amusement. Yo-yos and other toys have long been popular, but of limited variety. The new mechanism offers many possible alternatives for new toys or similar devices.